Diastereoselective alkylation of α-amino-substituted benzyllithiums

Reductive lithiation of a distereoisomeric mixture of bicyclic oxazolidines followed by reaction with alkyl halides afforded aminoalcohols in a highly syn-selective fashion. Reductive lithiation occurs with racemization at the benzylic carbon atom; the observed diastereoselectivities are rationalized in terms of a pair of rapidly equilibrating diastereoisomeric organolithium intermediates, one of which reacts preferentially under appropriate reaction conditions.